DESCRIPTION (provided by principal investigator): Late-onset Alzheimer's disease (LOAD) is a complex and multifactorial disease with the possible involvement of several genes. Apolipoprotein E (APOE), especially the APOE*4 allele, has been established as a strong susceptibility marker that accounts for 20-29 percent of the risk in LOAD. In addition to the disease risk, age-at-onset (AAO) of AD is also genetically controlled and the APOE gene accounts for <10 percent of the variation in AAO. This emphasizes the involvement of other genetic and/or environmental factors, which alone or in conjunction with APOE*4, can modify the risk or AAO of AD. Recently, genomewide linkage on LOAD have provided evidence for the existence of multiple putative genes for AD on several chromosomes with the strongest evidence on chromosomes 9, 10 and 12. With the construction of a high-density map of single nucleotide polymorphisms (SNPs) in the human genome, it is now possible to use the population-based association studies approach to identify the putative AD risk genes. A broad linkage peak encompassing >65 Mb region between chromosome 10q11 (at 50 Mb) and 10q25 (at 116 Mb) that influences both AD risk and AAO has been suggested. As part of our preliminary data we have screened 21 SNPs in 13 known biological candidate genes located under this broad >65 Mb linkage region in our large case-control cohort and identified suggestive significant associations with SNPs located in the choline acetyltransferase (CHAT) gene at 50.5 Mb on 10q11 and urokinase-type plasminogen activator (PLAU) gene at 75.3 Mb on 10q22 and thus our association findings are compliment to the reported linkage studies. This provides a strong rationale to comprehensively examine this linkage region by high-powered association studies to identify the chromosome 10 AD gene. The primary goal of this application is to comprehensively examine the ~65 Mb region between 10q11 and 10q25 first screening extensive panels of linkage disequilibrium (LD)-tagging SNPs in a first stage discovery sample to identify significant SNPs (Aim 1) and then confirm the significant findings in a second stage replication sample (Aim 2). The genes harboring confirmed significant SNPs in both stage analyses will then be comprehensively screened as part of Aim 3 to identify the putative functional SNPs.